The present invention relates to a multi-positional CT (computed tomography) image producing method and an X-ray CT apparatus, and more particularly to a CT image producing method and an X-ray CT apparatus capable of producing CT images at a plurality of positions in phase.
A conventional technique for producing CT images at a plurality of slice positions by an axial scan comprises, for each slice position, conducting an axial scan with the slice position registered with a central detector row of a multi-row detector, collecting a data set in a required view range at the central detector row, reconstructing a CT image from the data set, and repeating these steps for the plurality of slice positions.
Moreover, a technique for producing CT images at a plurality of slice positions by a helical scan comprises, for each slice position, conducting a helical scan with the center of a scanned range registered with the slice position, collecting a data set in a required view range, reconstructing a CT image from the data set, and repeating these steps for the plurality of slice positions.
On the other hand, there is known an image reconstruction method and an X-ray CT apparatus for conducting a scan while rotating an X-ray tube and a multi-row detector around a subject to be imaged to collect data, generating a data set in a predetermined view range by extracting data of projection points formed by projecting pixels on a reconstruction plane onto a plane of the multi-row detector in a direction of X-ray transmission, and producing a CT image based on the data set (for example, see Patent Document 1).
Furthermore, there is known a three-dimensional backprojection method comprising: extracting projection data corresponding to a projection line(s) formed by projecting one line or a plurality of parallel lines at spacings of a plurality of pixels on an image reconstruction plane onto a plane of a multi-row detector in a direction of X-ray transmission; generating projection line data by multiplying the extracted projection data by a cone beam reconstruction weight; generating backprojected line data by filtering the projection line data; determining backprojected pixel data of each pixel on the reconstruction field based on the backprojected line data; and determining backprojected data by adding the backprojected pixel data on a pixel-by-pixel basis for all views used in image reconstruction (for example, see Patent Document 2).
[Patent Document 1] Japanese Patent Application Laid Open No. 2003-159244.
[Patent Document 2] Japanese Patent Application Laid Open No. 2003-334188.
When a data set in a required view range is collected by an axial or helical scan at every slice position as in the conventional techniques, the phase at which the data sets are collected differs among the slice positions. That is, CT images at a plurality of slice positions have different phases.
However, in the case of making a comparative study of CT images taken through a plurality of slice positions of a heart, for example, the different phases among the CT images pose a problem of inconvenience.